Our aim is to understand how the normal adult human alveolar epithelial basement membrane regulates the differentiation of type II pneumocytes into type I pneumocytes. Our hypothesis is that the alveolar basement membrane plays an important role in the transformation. We have developed a model system in which isolated adult type II cells are cultured directly on an acellular human alveolar epithelial basement membrane. The lung matrix retains its 3-dimensional architecture; has intact epithelial and endothelial basement membranes. Type II cells attach to the epithelial basement membrane and subsequently transform into cells which morphologically resemble type I pneumocytes. Under similar conditions, the A549 cels retain cuboidal morphology. We plan to correlate the morphology and function of type II pneumocytes cultured on the lung matrix. We propose: 1) to utilize the model to study the morphologic transformation of type II pneumocytes into the type I-like form; 2) to study the effect of the alveolar basement membrane on the type II pneumocyte proliferation and their phospholipid profiles; 3) to develop monoclonal antibodies to freshly isolated adult rat type II pneumocytes after 3 days of culture on the lung matrix; 4) to utilize the monoclonal antibodies to identify type II pneumocytes and as functional parameters to follow the morphologic transformation of type II pneumocytes. The proposed studies will introduce new technologies for culture and identification of type II pneumocytes. The studies have potential for developing specific surface markers for type I cells. The studies are important for understanding: the development of the lung; the repair of lung epithelium after acute injury; the response of the alveolar epithelium in fibrotic diseases of the lung; and the mechanism by which the alveolar basement membrane controls normal epithelial cell functions.